The invention relates to a method for removing a tool from a hollow object and a tool for forming a hollow object.
The area of application of the present invention is in particular in the production of outer parts of constant velocity joints. As illustrated diagrammatically in FIG. 3, the outer part of such a joint has a substantially cylindrical inner surface. A plurality of sets of preferably helical grooves are provided, the grooves constituting helices of opposite hand. In order to simplify production, the grooves are normally straight and are inclined, for example at an angle of about 16xc2x0, with respect to the axis of rotation of the corresponding joint part, instead of being truly helical. Balls engage in the grooves and are held by a cage, and because of the crossed configuration of the grooves the balls are held in the angle-bisecting plane of the joint when the joint parts are articulated, giving the joint constant velocity properties. Constant velocity joints of this type are known as slip joints or cross-groove joints. As stated, these joints work with straight or helical grooves lying obliquely at an angle of for example xcex3=16xc2x0 to the axes of the driving and driven body.
FIG. 4 indicates diagrammatically how parts of this type are fabricated in practice. Starting from a slightly open position of the cup-like outer part, a so-called drawing-in movement is executed, during which the outer walls of the cup-shaped outer part are pushed inwardly, as indicated diagrammatically by arrows.
A method and a tool of this type are described in EP 0 270 538 B1. This known method is carried out using a tool having a ram with a first and a second set of ram segments which are mounted so as to be freely tiltable towards the ram axis, the second set of ram segments being supported on the first set of ram segments. The first set of ram segments can be spread by a mandrel, by which the second set of ram segments can also be spread indirectly via the first set of ram segments. After introduction of the ram in its working position into a hollow object situated in a die, the object is pressed by the ram through the die, the circumferential wall of the hollow object with grooves arranged therein in cross-groove configuration being drawn in and pressed against the ram segments arranged and formed in a manner corresponding to the grooves. After this drawing-in of the hollow object, the mandrel is first withdrawn, so that the first set of ram segments can move inwardly and be disengaged from the grooves. After this, the second set of ram segments, still present in the grooves, can then be pulled out of the hollow object axially, the ram having to be rotated in accordance with the hand of helix of the grooves.
This known method and the known apparatus are complex, both with regard to the design of the tool and with regard to the method steps for removal. The removal of the ram segments requires two successive removal operations, namely on the one hand the movement of the first set of ram segments into a released position and then the axial removal of the second set of ram segments, this having to be rotated with the ram in accordance with the hand of helix of the grooves. The known tool therefore has to be designed such that the ram can execute the specific helical movement. This requires not only a special drive, but also a special helical guide.
A further disadvantage of the known method and of the known apparatus is that the first set of ram segments is displaced into its released position by mechanical contact with the contours of the tool in the region of the grooves. Such a displacement contact leads, in a rapid operation, which is desirable, to impacts against the first set of ram segments as the ram is being rotated during removal and the first set of ram segments displaced into the released position by the displacement contact. Considerable stressing of the first set of ram segments and resultant wear both on the hollow object and on the ram are thereby inevitable.
The object on which the invention is based is to simplify a method of the type specified at the outset. In addition, the movement of the ram segments into the released position is to be improved.
In the case of the method according to the invention, all the ram segments are removed into their released position by contracting movements, so that a rotary movement of the ram can be dispensed with and the pushing-in movement of the ram segments is sufficient to remove them. Through a further axial relative movement between the hollow object and the ram, these parts can be moved away from one another axially in a simple manner, whereby the hollow object is separated from the ram.
The method according to the invention can therefore be carried out with a significantly simpler tool, since a helical movement for the ram including an associated guide is not required.
The tool here can be designed such that during removal the ram segments are displaced from the grooves owing, for example, to an axial movement of the ram segments, or an active pushing-in device can be provided as part of the tool, which device actively displaces the ram segments into their released position, thereby avoiding a displacement contact and resultant wear between the ram segments and the hollow object.
The further object on which the invention is based is to design a tool such that the ram segments can be removed without displacement contact with the hollow object.
In the case of the tool according to the invention, at least some of the ram segments are assigned a pushing-in device which is part of the tool and which moves the associated ram segments into their released position. If, in the case of the tool according to the invention, only some of the ram segments, namely the ram segments of one hand of helix, are moved into the released position by the associated pushing-in devices, the remaining ram segments of the other hand of helix can be removed by axial unscrewing, as is the case in the prior art. Preferably, all the ram segments are in each case assigned a pushing-in device, so that no unscrewing is required. In the case of the design according to the invention, no displacement contact therefore takes place during removal between the ram segments concerned and the hollow object, and wear on the ram segments and on the hollow object resulting from the displacement contact is therefore also eliminated, as are disruptions resulting from the displacement contact.
The subclaims contain features which further simplify and improve both the method and the tool. It is thus possible, for example, to derive the pushing-in movement from an axial movement of ram segments concerned, so that no special independent drive is required for the ram segments. It is furthermore advantageous and simplifying in this regard to bring about the axial movement of the ram segments by an axial movement caused at the hollow object. The stripping of the hollow object from the ram is thereby simplified and accelerated. Further features in the subclaims lead to simple, small, operationally reliable and inexpensively producible constructions which can be very advantageously integrated into a ram.